Telephone-transmitter



(No Model.)

I. H. FARNHAM.

TELEPHONE TRANSMITTER.

No. 380,752. Patented Apr. 10, 1888.

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N. FETERS, Fhamumo m mr. wnshmglnn, D4 cv NITED STATES PATENT OFFICE.

ISAIAH HENRY FARNH AM, OF MALDEN, ASSIGNOR TO THE NEW ENGLAND TELEPHONE AND TELEGRAPH COMPANY, OF BOSTON, MASSACHUSETTS.

TELEPHONE-TRANSMITTER.

SPECIFICATION forming part of Letters Patent No. 380,752, dated April 10, 1888.

Application filed November 26, 1887. Serial No. 256,200. (No model.)

To all whom it may concern.-

Be it known that I, ISAIAH HENRY FARN- HAM, of Malden, in the county of Middlesex and State of Massachusetts, have invented certainImprovementsinTelephone-Transmitters,

of which the following is a specification.

This invention relates to telephone-transmitters,and especially to those wherein the essential variations of current are effectuated by corresponding variations of resistance of a mass of finely-divided granulated or powdered carbon or like material in a loose and free state when the said granulated material is subjected to the influence of a vibratory diaphragm controlled by the impact of the soundwaves of the human voice. These sound waves are usually directed upon the said diaphragm or vibrating plate through a suit-able mouthpiece shaped internally into the wellknown vocalizing or air-condensing chamber. The diaphragm generally constitutes one electrode of the circuit in contact with the granulated material,and there is also a complementary electrode, which in some instances forms the back plate of the inclosing-chamber, and in other cases is buried wholly or partially in the currentvarying material. Transmitters of this general type have been found to have a tendency to lose a great part of their power after they have been left unused for some time, and also occasionally when in active use, and this defect has usually been ascribed to packing of the inclosed granules. Experiments have, however, indicated that a certain portion of the trouble is due to the heating of the particles upon the passage of a battery'current, and, furthermore, that the packing, if it may be so called, which does occur, is not due to any inherent tendency on the part of the particlesto become solid or to subside and cohere in a mass at the lower part of the chamber, but to a too close and rigid confinement of the said particles, or in other forms to too great a weight placed upon the mass, causing it to press too hard against the electrodes or diaphragm.

Considerable thought has been given to the invention of devices or forms to prevent packing, and, among other ideas, that of a comple- 50 mentary electrode completely embedded in the mass of grauulations and associated with a horizontal diaphragm supporting the said granulations on its upper surface has been employed. The complementary electrode has also been constructed of various forms, and 5 has been arranged to depend from the back plate of such a transmitter downward into the diaphragm supported mass. I have, however, obtained excellent results and an entire absence of packing in the use of the invention I am now about to describe, in which the pendent electrode is dispensed with, and in which, although a horizontal diaphragm is employed, it does not sustain the granulated mass, but surmounts the same.

This invention is a telephone-transmitter comprising a mass of conducting granulations, preferably,of course,of carbon, inclosed loosely in a suitable case with non-conducting sides or walls upon a mobile or elastic and extensi- 7o ble bottom, the complementary electrode being buried in or stretched through said mass, which is surmounted by a horizontal Vibratory diaphragm and mouth-piece.

It also comprises means for adjusting the elastic and extensible floor or bottom, and for so expanding and raising its center as to diminish the carbon-holding space and to press the carbon therein up against the under surface of the diaphragm.

It also provides that the said elastic floor shall also be elastic or resilient, either inherently or in virtue ofa spring located between its center and the means for adjustment, whereby not only can the containing-cavity be readily regulated as to size, but, being also made with one of its sides (and specifically the side opposite to that which receives the impact of the sound-waves) perfectly and delicately elastic, the inclosed carbon is enabled to aco commodate itself to variations caused by heating, shaking, &c., and an intimate contact can furthermore always be maintained between the diaphragm and the upper surface of the carbon mass, although the diaphragm sur- 9 5 mounts instead of supporting the said mass; and I find that the diaphragm, thus freed from the dead weight of the superimcumbent mass, is enabled to follow more accurately the variations of the transmitting sound-waves,andthat I00 the entire instrument as a transmitter is thus capable of causing variations in the electrical current traversing the circuit, which copy with great accuracy the original sounds. These improvements can furthermore be adapted to the ordinary Hunnings transmitter.

In the drawings which accompany this specification, Figure l is a perspective view of one form of a transmitter embodying my invention. Fig. 2 is a sectional View in elevation of the operative parts of the instrument shown in Fig. 1. Figs. 3 and 4 are detailsof Fig. 2. Fig. 5 is aformshowingaslight modification of the rear and mobile wall or floor of the transmitter; and Fig. 6 is a portable form of transmitter embodying the invention, and partly in section.

It must be understood that the invention is independent of external form.

In the perspective view the transmittera is mounted on the vertical standard I), this in turn passing at itslowcr end through thebaseplate 8. suitable baseboard, c, of wood or like material, on which, if desired, may also be placed the induction coil A, attached by means of bands 8, or otherwise.

If an induction-coil be used, the line-wires or line and ground wires are to be attached to binding-screws 6 and 7, one of which represents one end of the secondary coil direct,while the other connects with the other end of the secondary coil through the receiving-telephone T, which has its conductors connected with binding-screws 2 and 3. The battery is connected with binding-screws iand 5. The vertical standard b is of metal, (brass, for exam-- ple,) and at its upper end makes contact with and is secured to the lower plate, 9, of the instrument-casing, which may also be of brass. The standard I) thus is made to serve as one of the conductors leading to the transmitter. This is, in a manner hereinafter to be described, brought into electrical connection through the casing of the instrument with one of the electrodes, while the flexible conductor 7, having one ofits ends fastened to the binding-screw g and the other in the base bindingscrew 1, constitutes the remaining transmitterconductor and connects with the other electrode. The primary or battery circuit may now be traced. Leaving one pole of the battery B, it passes to the binding-screw 4, and through successively the primary helix of the induction-coil, the flexible conductor r, the transmitter a, and the standard I), back to binding-screw 5, and thence to the remaining battery-pole. Of course this order of succession may be reversed or altered at will without affecting the operation.

Referring to Figs. 2, 3, and 4, it will be seen that the transmitter proper, a, consists of a containing-cell in form like a short cylinder, having a non-conducting side wall, a non-conducting, yielding,'elastic, and extensible floor, with a regulating device by which it may be raised at its center for the purpose of vary- The base-plate s is screwed to any ing the size of the chamber, and a flexible and vibratory diaphragm closing its front opening.

This cell incloses a mass of finely-divided granulated carbon or othersuitable granulated conducting material and,embedded therei n,a complementary electrode.

The transmitter is constructed as follows: The cylindrical side wall, f, is formed of any suitable hard nonconducting material, such as hard rubber, vulcanized fiber, or glass. I preferably use the latter material, as I find it convenient and not subject to material change with temperature variation. It is closed at the upper side by a very thin metal or carbon vibrating diaphragm, h, (if metal is used,platinum-foil gives the best results.) whichis held in place, closing or sealing the chamber, by a top plate, 6, formed internally with a shoulder to provide the necessary condensing-chamber, h, and having a central orifice, to which is fitted a mouth-piece, d, of any desired or convenient form. To this top plate is affixed the binding-screw q, whereby the diaphragm is brought through the said top plate into the circuit, the said diaphragm being thus caused to form one electrode of the transmitter. The other end of the non-conducting cylinder-section f is closed by the thin, yielding, elastic, and extensible floor or bottom I, which I prefer to make of very thin sheet-rubber. This is cut to the proper size, and is laid on the lower metal case'plate, g. This plate may also form the support of the complementary electrode j, which, as shown in Fig. 3, may be a metal disk having a number of holes, 0, drilled through it, and which can be mounted upon a metal standard, 2', screwed or bolted at k to the case-plate g, as in Figs. 2 and 5. The center of the plate 9 is also perforated, and the perforation is threaded for the reception of an adjusting-screw, m, having a set-nut, a, and a button, m, on its inner end, which button presses upon the center of the lower surface of the rubber sheet. Good results are attained by so proportioning the various parts that the fixed electrode j is when in place about onetenth of an inch below the diaphragm. The other proportions may be greatly varied without interfering with the efficient operation of the instrument, as is well understood by those skilled in the art. By means of the adj usting-screw m, which passes through the baseplate 9, I am enabled to readily operate the adjustment of the mobile floor-sheet. The bottom case-plate, g, with the elastic floor or end wall, l, and the fixed electrode j, is clamped or bolted to the upper plate, e, by suitable bolts or screws 1), these being insulated from the upper plate by nonconducting washers or bushings 3 thus forming a closed chamber. WVithin this chamber,

and between the vibrating diaphragm h and the elastic floor-sheet Z, is placed the granulated carbon, 10, in a quantity sufflcient to fill, or nearly so, the cavity. When the chamber is being filled, the diaphragm and top plate will be taken off and the adjusting-screw turned down, and the granulations, on being poured in, will flow round and through the holes of the electrodej. The initial adjustment is obtained by turning up the adjusting-screw, which, by forcing up the center of the elastic diaphragm, decreases the carbon-space above it, and thereupon brings the carbon into permanent but gentle and elastic contactwith the diaphragm-surface.

It will be readily understood that the provision of such a yielding elastic bottom or floor, besides making feasible the arrangement of the diaphragm above the carbon, whereby it is enabled (being relieved from pressure) to vibrate more freely, allows the granular particles to accommodate themselves to varia tions caused by heating or shaking, and prevents too great variations, such as would be caused by an actual break of contact, much in the same way as in the spring adjustment of the well-known ordinary Blake transmitter. It is evident that this necessary elasticity or resiliency of the bottom wall or floor may either be in virtue of an inherent property of the material ofsaid floor or may be artificially imparted thereto by a suitable reenforcing spring.

Fig. 5 shows a form in which the latter plan is utilized. This is similar in principle with the form'shown in Fig. 2; but, instead of employing an extensible and elastic material for the floor of the chamber,Iemploy a sheet of silk or cloth fabric left rather slack, interposing a suitable spring, 1, between the center of its lower surface and the end of the regulatingscrew, the spring in this case acting as the elastic cushion and keeping the cavity of proper size.

In Fig. 6 my improvement is shown applied to the older form of Hunnings transmitter. In that instrument the granulations were confined between a back and front plate of metal, the front plate being vibratory and serving as the diaphragm. The only change necessary is to mount the back plate with a cavity in its rear and to make holes or openings therein through which the granules can circulate, and then to close the rear cavity with the elastic and extensible rear wall which I have described.

In the drawings, a is the handle, 9 the chambered case, and d the mouth-piece fastened to the cover 6, which can be screwed or otherwise fastened to the case 9, thereby clamping the edges of the diaphragm h. The perforated back plate, of metal or carbon, 10, is fitted in.

a shouldered recess of the case, and is separated electrically from the diaphragm by a non conducting ring, 2. Therear ofthecavity is closed by the elastic wall Z, controlled and adjusted by the screw m, as in the other examples. The granular conducting matter 10' is inclosed in the chamber between the diaphragm and rear wall and circulates on both sides of and through the holes of the plate to. 3 and 4 are the connecting-wires, andlead one to the diaphragm and the other to the plate 10.

On short circuits this transmitter can of course be used, included directly in the line circuit with a battery; but for long circuits the induction-coil is preferably associated with it. In the latter form, as well as in the forms first described, it is to be understood that the only connection of an electrical character between the diaphragm and the complementary electrode is to be made through the carbon mass. This feature, secured in the forms shown in Figs. 1, 2, and 5 by insulating the boltsp from the upper plate, is in Fig. 6 attained by the interposed ring 2.

1. The combination, in a telephonetransmitter, of a containingchamber having rigid non-conducting walls and a mobile, resilient, and extensible rear wall or floor closing the lower end thereof, a mass of granulated or finely-divided conducting material inclosed within said chamber and upon the said floor, a horizontal flexible vibratory diaphragm surmounting the said mass, closing the other end of said chamber, and constituting one of the electrodes of a circuit, a second or complementary electrode embedded or buried in the finely-divided conducting material, and an adjusting device for the extensible rear wall, whereby the said wall may be extended into the interior of the chamber, thus diminishing the capacity thereof, and for the purpose of maintaining permanent butelastic connection between the diaphragm and conducting mass, substantially as hereinbefore described.

2. The combination, in a telephonetrausmitter of the type or class hereinbefore speci-,

fied, of a mass of granular carbon, a cell or chamber with vertical non conducting side walls confining said mass, a horizontal conducting-diaphragm stretched over the said granular mass, a mobile or elastic and extensible floor closing the cell at its lower end and supporting the granular mass upon its upper surface, and an adjusting device acting upon the center of the said extensible floor and adapted to elevate the same into the interior of the chamber, thus contracting the space thereof, whereby an initial contact is maintained between the carbon and the diaphragm, and whereby an elastic cushion is also pro vided for the carbon mass, as described.

3. In a telephone-transmitter of the character hereinbefore referred to, the combination of a containing-chamber with nonconducting side walls, a flexible, vibratory, and conducting diaphragm closing one end of said cham' her and serving as one electrode, an elastic and extensible non-conducting floor or rear wall closing the other end of said chamber, an adjusting or regulating screw controlling the said elastic rear wall and adapted to force the center thereof into the interior of said chamher, a mass of granular or finelydivided carbon inclosed within said chamber, and a complementary or fixed electrode perforated for the free passage of the carbon particles and mounted or stretched within the said chamber ICC IIO

and through the mass of carbon between the diaphragm and rear plate, substantially as specified.

4. The combination, in a granular-carbon transmitter, with a cell containing the granules, of a flexible metal vibrating diaphragm closing one end of the said cell and connected with one end of an electric circuit, a fixed electrode inclosed in said cell, extending through and in contact with the carbon granules, and connected with the other end of an electric circuit, a mobile and resilient rear wall or floor closing the other end of the said cell, and adjusting devices acting upon the said elastic floor and adapted to raise the center thereof into the interior of said cell for the purpose of initially compressing the granules to the requisite degree, and of establishing and maintaining elastic and yielding contact between the diaphragm and the carbon granules and between the respective granules, as described herein.

5. In a telephone-transmitter of the hereinbefore-described character, the combination, with a loose mass of conducting particles confined within a chamber having a rigid and vertical side wall,and a conducting and flexible diaphragm sin-mounting the said mass, of an elastic cushion closing the lower end of said chamber and forming the floor thereof, upon which the said mass rests, and whereby the said mass may be retained in yielding but permanent contact with the surmounting diaphragm.

6. A telephone-transmitter comprising the following elements: a containing-cell having rigid non-conducting side walls, a metal cappiece therefor, and a flexible conducting vibratory diaphragm clamped thereby to the upper edge of the said side walls, a mouthpiece fitted to an orifice in the center of said cap-piece, a metal plate fitted to the lower edge of the cell,constituting a portion of the outer case thereof and closing the same, a com plementary perforated electrode mounted upon a standard fixed to said plate, a sheet of thin elastic rubber or its equivalent stretched over the inner surface of said plate, a mass of granular or finely-divided carbon inclosed in said cell between the rubber sheet and flexible diaphragm and surrounding the perforated electrode and an adjusting-screw extending through the closing case-plateand bearing upon the center of the rubber sheet, whereby the same may be projected forward into the cell for the purpose of establishing and adjusting contact-pressure between the carbon particles and the diaphragm and to provide an elastic cushion for the said particles, substantially as described.

7. A telephone-transmitter comprising the following elements infcombination: a containing-cell in the form of a short cylinder .having rigid vertical non-conducting side walls, a metal cap-piece therefor centrally perforated for the reception of a mouth-piece, ahorizontal platinum vibrating diaphragm clamped to the upper edge of said cylinder, a sheet of thin elastic rubber, serving as the rear wall,

bottom, or floor of the containing-cell, and 7c clamped to the lower edge of the vertical wall thereof by a metal plate, which plate 1s bolted to but insulated from the cap-plece, a fixed or complementary electrode suspended or mounted within the cell at a suitable distance from the diaphragm and in electrical connection with the said lower metal plate, a mass of finely-divided carbon in a loose and free state inclosed within the said cell and upon the rubber floor thereof, and an adjusting device for the said carbon and rubber floor, consisting of a screw projecting through the lower metal plate against the center of the said rubber floor, whereby the said fioor-center may be elevated and the carbon particles elastically compressed with respect to one another and brought into permanent and resilient contact with the horizontal diaphragm which rests upon the upper surface of said particles, as described.

8. In a granular carbon transmitter, a carboncontaining cell with vertical non-conducting side walls having a flexible conducting-diaphragm to close its upper end, and an adjustable elastic floor closing its lower end, upon which the carbon particles rest within the chamber, and whereby they can be moved into and maintained in elastic contact with the diaphragm, for the purposes specified.

9. In a telephone-transmitter of that class in which the current -varying material-is a mass of finely-divided carbon in a loose and free state, a horizontal and flexible conducting-diaphragm, and a carbon-holding chamber mounted immediately thereunder, clamped to the edges thereof,having rigid non-conducting side walls, and provided with a spring floor or rear wall supporting the mass of carbon, the central portion of which door is adjustable by means of a screw with respect to the diaphragm,whereby the said mass of carbon may be caused to make an initial but elastic and variable contact with the diaphragm, substantially as and for the purposes specified herein.

10. In a telephone-transn'iitter of the hereinbefore-described type or class, a horizontal vibrating diaphragm and a carbon-holding cup supported below the said diaphragm and provided with an elastic and extensible springbottom, upon which the inclosed mass of carbon rests, and whereby the said carbon may be maintained in intimate but elastic contact with the said diaphragm.

In testimony whereof Ihave signed my name to this specification,in the presence of two subscribing witnesses, this lSth day of November, 1887.

ISAIAH HENRY FARNHAM.

Witnesses:

GEO. WILLIs PIERCE, FRANK G. LocKwooD. 

